Scanning radio receivers are well known in the art and have improved and evolved with the ever higher level of circuit integration available in modern electronic technology.
It is common for a modern scanning radio to comprise a microcontroller or microprocessor with memory and phase-lock-loop frequency synthesizer, so that a great number of frequencies can be received and, if desired, stored in a channel memory. It is common for scanning receivers to comprise two hundred or more storage locations in its channel memory. It is also common for modern scanning receivers to receive a very wide bandwidth of frequencies. Receivers are capable of receiving from 29 MHz to over 1 GHz in channel increments of 5 kHz, 12.5 kHz, and 25 kHz, for example.
A common operational mode for such a scanning receiver is to scan a desired band of frequencies and listen for desired signal transmissions. Upon hearing such a signal, the user can manually program the received frequency into a channel memory, so that the frequency can be subsequently scanned for reception of signal transmissions. A plurality of frequencies may carry related signal transmission and therefore it is desirable to scan a group of frequencies, or channels, in order to receive all of the related signals. For example, the aircraft band comprises the frequencies ranging approximately from 108 MHz to 137 MHz. Various frequencies in this band may or may not carry signals depending of the geographic location and air traffic in that area. Because of this grouping of frequencies, modern scanning receivers have channel memories which group a plurality of channel memory storage locations into banks of storage locations, or channels, which can be selectively scanned. For example, a first bank may be programmed with frequencies in the aircraft band. A second bank may be programmed with frequencies from the 70 cm amateur radio band, etc. When a user desires to scan a particular group of channels, known to carry intermittent signal transmissions, the user merely activates a bank of channel memories which had been previously programmed with the desired group of frequencies.
The task of programming the various frequencies which regularly carry intermittent signals into a channel memory can be a difficult task. Considering, in the foregoing example, that the band of frequencies from 108 MHz to 137 MHz is divided into approximately 2300 discrete frequencies.
To alleviate and simplify this problems, certain publications are available which tabulate the frequencies for various types of services in particular geographic areas. Scanner users can refer to this type of publication to select frequencies and program channels into a scanning receiver, so that the desired channels can be scanned to monitor the desired communications signals. However, the use of such a publication is not an ideal solution nor a particularly convenient method of programming channels into a scanning receiver. Frequently, there are a large number of channels listed for a particular service type, and, many of these channels are essentially idle. If a user programs all of the channels for a particular service type into the scanning receiver, then many of the scanner channel memory storage locations will be filled with channels that have very little chance of carrying desirable signals. Furthermore, when the scanner is scanning the plurality of programmed channels, time will be wasted scanning the aforementioned channels. As such, desired communications signals will not be received during the time the idle channels are scanned. Also, the Federal Communications Commission continually licenses new users in the various bands so that no publication listing frequency allocations can be completely up to date.
Other communications receivers have been devised which scan for the presence of a signal and so note the presence of such signals. Modern television sets, for example, have automatic channel search features which scan all the channels which are receivable by the receiver and record the existence of signals on each of the channels on which they are found. However, such a scheme relies on the fact that a continuous signals is being broadcast at a particular frequency, allowing the automatic channel search feature to find the signal at the moment it receives a particular frequency. In the situation of a broad band scanning receiver, however, most of the transmitted signals are not continuous, but rather intermittent. Therefore, the channel search features as described above will not be suitable.
Clearly, there is a need to simplify the process of programming frequencies from within a given band of frequencies, that carry intermittently transmitted signals, into a channel memory.